As a OG OneNote fan, OneTastic is an absolute must if you are serious about using OneNote. It expands OneNotes functionality, allows serious customization and of course, automates repetitive tasks. It's also easy to build your own macros.
If you use OneNote desktop ... you have to use Onetastic! Adds amazing features such as Table of Contents, Sorting, Calendars, backgrounds... so much more! I use it daily.
DataQlick